Engine governing devices previously used for internal combustion engines, to prevent excessive wear and engine damage, have been of two general types. A first type operated to shut off the ignition and prevent the spark plugs from igniting when overspeed was detected, while a second type reduced or eliminated fuel flow to the engine. Both of these approaches to engine governing suffered from the same problem, namely, they both failed to maintain the desired air/fuel ratio during the governing time. With the first type of governor, described above, the effect of shutting off the ignition allowed the combustible fuel/air mixture to pass out of the engine unburned. This resulted in a harmful and potentially dangerous mixture being expelled from the engine exhaust system. Hydrocarbon emissions were often extremely high, while a dangerous potential exists for igniting the mixture accidentally and causing backfiring or a fire. With the second type of governing, a shut off or reduction in fuel flow upon detection of overspeed also created severe problems. Since the fuel reduction was not accompanied by a similar airflow reduction, the air/fuel ratio became uncontrolled, resulting in the generation of harmful or dangerous emissions. Although cutting the fuel entirely reduced emissions, this approach created two other problems. First, the engine lost all power when fuel was cut entirely off. When the engine speed dropped, the governor turned on fuel again. When repeated, this caused the engine to be cycled from minimum to maximum power constantly. The result was poor performance and potential engine and vehicle damage. The second problem of the fuel-cut strategy was that in the transients between minimum and maximum power, the air/fuel ratio was incorrect, thereby resulting in the generation of substantial harmful emissions.
In an electronic engine control system wherein a driver's command from the accelerator pedal is furnished to a computer control unit instead of being linked directly to the throttle, the aforesaid problems of governor control become even more complex. The present invention effectively solves these problems in a computer controlled system for a fuel injected internal combustion engine wherein airflow is controllable to match the fuel supplied as a result of a modified fuel command signal.
Another important aspect of the engine governing problem is that of determining the maximum allowable speed limits for different engine operating and environmental conditions. Although a single fixed maximum engine speed value could be selected, it might not be ideally applicable for varying abnormal conditions, e.g., low temperature. Thus, it is preferable that the governing system automatically select the safe operating maximum speed level and keep it up to date with changing engine and environmental conditions. The present invention also solves this problem by providing a system whereby the governed speed will never exceed the presently determined maximum allowable speed of the engine.
It is, therefore, a general object of the present invention to provide an improved governing control for a fuel injected internal combustion engine in order to reduce the possibility of damaging the engine through intentional or benign abuse.
Another object of the present invention is to provide a governing system for a computer controlled internal combustion engine wherein airflow is controllable to match the fuel supplied as a result of a modified fuel command signal that is generated to provide an engine speed below the maximum allowable speed.
Another object of the present invention is to provide an improved governing control system for a fuel injected internal combustion engine wherein engine speed is controlled by automatically varying fuel flow rate and airflow to maintain an optimum air/fuel ratio so that no harmful emissions are generated and adequate engine power is maintained during the governed period.
Yet another object of the invention is to provide a governing system for an internal combustion engine wherein the maximum allowable engine speed for the existing engine condition is first ascertained automatically and also the fuel flow rate necessary to maintain such maximum allowable speed, the latter being used only if the simultaneous driver command fuel flow rate is higher.
Another object of the invention is to provide an automatic engine control system with an engine control unit which utilizes driver command signals equivalent to a desired fuel flow rate while automatically controlling airflow proportional to the fuel flow and which automatically determines a maximum allowable engine speed and then prevents the driver command signals from exceeding the maximum allowable speed despite the magnitude of driver command signals received.